It's called narcissistic personality disorder - inspired by a mythical character who fell in love with his own reflection - and its symptoms are a preoccupation with one's own success, power and brilliance coupled with a singular lack of empathy for others.

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"[Turnbull's] got narcissistic personality disorder. He says the most appalling things and can't understand why people get upset."

Should we be surprised?

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An expert on the condition thinks our political landscape is dotted with Narcissus-like characters.

"The truth is that, in order to be a politician, you'd have to have a degree of narcissism," University of NSW Associate Professor Carolyn Quadrio says.

"It's a rough game and you're getting battered all the time.

"Each time you go to an election you do so knowing roughly half the people will vote against you.

"If you're fragile you're not going to survive."

The Mental Health Association of NSW says people with narcissistic personality disorder have a "grandiose view of themselves, a need for admiration and a lack of empathy that begins by early adulthood and is present in various situations".

In order to be successful a certain amount of narcissism is an essential part of the make-up, that and some obsessionality

Professor Quadrio, who studied narcissism in doctors who began sexual relationships with patients, said there was no way of telling whether Mr Nelson's diagnosis of Mr Turnbull was accurate.

"We can all be described as having these characteristics to some extent ... it's only when they become very marked or fixed ways of behaving that you say someone's got a clinical disturbance," she said.

But some narcissistic tendencies, plus a good dose of obsessive behaviour, are prerequisites for political life, Professor Quadrio said.

"In order to be successful a certain amount of narcissism is an essential part of the make-up, that and some obsessionality," she said.

Professor Quadrio singled Prime Minister Kevin Rudd, as well as Mr Turnbull, as having obvious but "healthy" narcissistic streaks.

Mr Rudd, in particular, was often portrayed in the media as obsessive and coldly ambitious.

"He's characterised in a way that suggests very strong obsessional ways, that need for organisational control and detail," Professor Quadrio said.

"[Politicians] are often [perfectionists], they're sticklers for detail, devoted to work and working hard, and they're very concerned with productivity and they're often quite inflexible."

Liberal frontbencher Tony Abbott came to his leader's defence yesterday on the ABC's Insiders program, telling the host: "You wouldn't go into Parliament if you didn't have a pretty solid ego."

Professor Quadrio said it was possible politicians present as narcissistic simply because the community finds absolute conviction attractive.

"If you have a very sure sense of yourself and that what you're doing is right and wonderful, that fuels ambitious behaviour," Professor Quadrio said.

"You want a leader who has the courage of their convictions but when it gets to the point when they're destroying everyone who gets in the way, that's too far."

She said the disorder is diagnosed when narcissistic traits become so pronounced they harm the person's life or the lives of people around them.

“If someone's so convinced they're right and everyone else is wrong and the only way of doing something is their way, you'd say then that someone's sense of their way being the right way has gone berserk," she said.